The present invention relates to a parallel scan thermal camera including a chip of infrared detectors disposed in lines and a chip for processing the detection signals including means for integrating the output currents of the detectors and delivering charge amounts associated with each of the lines of detectors.
Such a camera is used nowadays more particularly in the image formation field, for analysing landscapes in real time for example.
For a uniform illumination or background, the charge amounts vary from one line of detectors to the other, which contributes to creating the phenomenon of false contrast, or fixed spatial noise, and which adversely affects the quality of the images. This noise in fact originates in the dispersion of the currents delivered by the different detectors because of the variations of
the cut off wavelengths,
the dark currents,
the impedances,
the quantum efficiencies and sensitive areas,
the bias voltages.
To avoid saturation of the processing circuits by this phenomenon and so that the quality of the images obtained is not spoiled too much, a certain dynamic is then required with respect to the noise level, to which must be added the dynamics proper to the detection signals which depends on the temperature differences considered.
For solving the problem raised by fixed spatial noise, it might then be considered desirable to store the different false contrast charge levels, preferably in digital form, before proceeding to a comparison with the charge levels of the detection singals. Considering the above mentioned dynamics, in practice of the order of 1000, an analog/digital (A/D) conversion of the signals would then be required which is compatible in accuracy, i.e. over 11 or 12 bits and at a high speed, namely over a period of the order of 500 to 600 ns if 18 lines of detectors are scanned in 10 .mu.s.
There exist at the present time on the market A/D 8 bit-500 ns converters but no 12 bit converter.
The present invention aims at filling this gap.